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Printability of ink used
Release time:
2022-06-23 17:58
The performance of the substrate, printing ink and other materials matching the printing conditions and being suitable for the printing operation is called printability. The printability of ink refers to the performance of the ink matching the printing conditions and being suitable for the printing operation, mainly including viscosity, adhesion, thixotropy, dryness, etc.
Viscosity
The internal friction characteristics of the ink during flow are called the viscosity of the ink, and the physical quantity that measures the viscosity of the ink is called the viscosity of the ink. The faster the speed of the printing press, the greater the fluidity of the ink is required and the smaller the viscosity. The viscosity of the ink can be adjusted with ink oil or ink diluent.
Adhesion
When the ink is transferred from the ink fountain to the ink roller, printing plate, substrate (or rubber cloth) surface, the ink film first splits and then transfers. The ability of the ink film to prevent the ink film from breaking in this dynamic process is called the adhesion of the ink. During the printing process, if the adhesion of the ink does not match the performance of the substrate and the printing conditions, the paper will lose powder and hair, the ink will not be overprinted well, and the printing plate will be dirty. The adhesion of ink can be adjusted with detackifier or ZY ink additive.
Thixotropy
At a certain temperature, the fluidity of ink is improved and the viscosity decreases after stirring or applying mechanical force; after standing, the fluidity becomes poor and the viscosity increases. This property is called the thixotropy of ink. During the printing process, if the thixotropy of the ink is poor, printing failures such as poor ink flow, uneven ink transfer, and severe dot expansion will occur. In order to prevent the occurrence of the above failures, it is necessary to stir the ink in the ink fountain frequently with an ink shovel or install an ink agitator in the ink fountain to stir the ink from time to time.
Drying
There are three main forms of ink drying.
Penetration drying: Part of the binder in the ink penetrates into the substrate, and the other part is fixed on the surface of the substrate together with the pigment and dries. Non-thermosetting rotary inks used in high-speed web printing presses are generally based on penetration drying, mainly printing newspapers and periodicals.
Oxidative polymerization drying: The binder in the ink undergoes polymerization reaction under the action of oxygen in the air, forming a film on the surface of the substrate and drying. Offset glossy resin ink has bright colors and good gloss. It is mainly dried by oxidative polymerization and is used to print high-end and fine offset products.
Volatile drying: Part of the binder in the ink evaporates into the air, and the remaining binder and the pigment are fixed on the surface of the substrate and dried. Gravure printing ink uses volatile solvents as binders, and the binders used are benzene and xylene, which are harmful to the human body. Volatile drying ink is particularly suitable for printing non-absorbent film materials, such as plastic films, metal foils, etc.
In addition, there are many forms of ink drying, such as ultraviolet rays, infrared rays, and thermal curing. The drying of many inks is often a combination of two drying forms to complete the drying of the ink film.
During the printing process, if the ink is not dried well, it will cause printing failures such as dirtying on the back of the paper, sticking to the page, dull ink film, and ink crystallization. In order to speed up the drying of the ink, a drying agent can be added to the ink. Commonly used drying agents include cobalt drying oil, manganese drying oil, lead drying oil, etc. In order to reduce the drying speed of the ink, a drying inhibitor can be added to the ink.
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